But even if McDonald's fries don't start getting tagged in photos, brands can still take advantage of facial recognition software. In fact, they already have outside of Facebook.

Last year, the Los Angeles Times reported that advertisers, including Kraft and Adidas, were considering using in-store facial recognition technology to tailor their pitches to potential customers so that they can use age and gender to direct them to the appropriate product. The Venetian hotel and casino in Las Vegas, for example, already uses it in digital displays to suggest different entertainment options to different demographics (although the technology is less helpful for 25-year-olds sporting senior citizen-like vintage duds).